This is actually quite easy. Lookup how to purchase a home with cash (its easy). The house is then assigned to an owning entity to become part of a portfolio. Then after a given time based on risk you can sell to generate revenue. Then disburse to other entities that lead back to the person that dropped in the cash. The wash is completed. Where else could you drop large quantities of cash then translate that to clean money?

In very specific cases it can be used to avoid certain countries' laws about exporting cash/value.

But that's not going to be a major source of real estate transactional volume.